In recent years, Thin Provisioning, which employs a virtual volume without its own storage area (hereinafter referred to as the ‘virtual volume’), has come into widespread use for the purpose of simplifying operations management and unifying storage environments as storage environments grow larger and more complex due to increased amounts of enterprise data.
With Thin Provisioning, if a virtual volume is presented to a host device and there is write access by the host device to the virtual volume, a physical storage area for actually storing data is assigned to the virtual volume. As a result, the storage area in the storage apparatus can be used efficiently while a volume of a capacity equal to or greater than the storage area in the storage apparatus is presented to the host device.
In addition, the storage apparatus comprises a plurality of hard disk drives (HDD) for storing data according to write access by the host computer. Furthermore, through RAID (Redundant Arrays of Independent Disks) technology, the storage areas of the plurality of hard disk drives are made redundant and a RAID group is configured. Physical disks of the hard disk drives and logical volumes which are segmented from a portion of the storage area of the RAID group are used as volumes which are recognized by the host computer for the storage of data.
In order to facilitate management of these volumes and management of the volume capacity, PTL 1 discloses a technology known as the ‘external connection function.’ With the external connection function, a volume provided by a second storage apparatus (hereinafter referred to as the ‘external storage apparatus’) which is connected to a first storage apparatus can be associated with a virtual volume provided by the first storage apparatus. Hereinafter an association of a volume provided by the external storage apparatus with the virtual volume will be called an external connection.
Furthermore, if an I/O request for a virtual volume transmitted from the host computer is received by the first storage apparatus, the I/O request can be transferred to a volume of an external storage apparatus which corresponds to the virtual volume. As a result, when the system administrator provides the volumes of the storage apparatuses to the host computer, since only the first storage apparatus may be managed, management of the volumes can be facilitated by centrally managing the volumes. In addition, by presenting a virtual volume to the host computer, the amount of storage areas which are handled by the first storage apparatus can undergo an apparent increase.
Accordingly, if there is a request to assign a volume to the host computer, even when there is insufficient unused capacity in the volume of the actual storage apparatus, volume in the designated capacity can be provided from an externally connected storage apparatus. Furthermore, a volume on the same tier as the tier of the designated volume can also be provided by means of an external connection.